The present invention is directed to improvements in the silver halide based photography.
The principle of silver halide photography is based on the activation of silver halide grains by light. A method to reduce the amount of silver present, without loss of the specific surface area of the grains in the photographic layers, is realisable by the use of tabular grains. Tabular grains in general (for which the diameter is considerably larger than the thickness) are also preferred for raising the speed of a silver halide emulsion for photographic purposes, increasing sharpness, and improving graininess, colour sensitivity efficiency with sensitising dyes and covering power. The high bromide {111} tabular grains are commonly used in the photographic industry. Still, there is a need to produce tabular crystals with a high aspect ratio and a narrow size distribution. A Grain Growth Modifiers (GGM) can narrow the size distribution and increase the aspect ratio.
Definitions
In the present description the following terms and definitions are used.
In referring to grains and emulsions containing one or more halides, the halides are named in order of ascending concentrations
The term xe2x80x9chigh chloridexe2x80x9d in referring to grains and emulsions indicates that chloride is present in a concentration of greater than 50 mole percent, based on total silver.
The term xe2x80x9chigh bromidexe2x80x9d in referring to grains and emulsions indicates that bromide is present in a concentration of greater than 50 mole percent, based on total silver.
The term xe2x80x9cequivalent circular diameterxe2x80x9d or xe2x80x9cECDxe2x80x9d is employed to indicate the diameter of a circle having the same projected area as the silver halide grain.
The term xe2x80x9caspect ratioxe2x80x9d designates the ratio of the grain ECD to the grain thickness.
The term xe2x80x9ctabular grainxe2x80x9d indicates a grain having two parallel grain faces which are clearly larger than any remaining grain face and an aspect ratio of at least 2.
The term xe2x80x9ctabular grain emulsionxe2x80x9d refers to an emulsion in which tabular grains account for greater than 50 percent of the total grain projected area.
The term xe2x80x9c{111} tabularxe2x80x9d is employed in referring to tabular grain emulsions containing tabular grains having {111} major faces.
Octahedral grains with respect to high chloride-containing grains means eight-sided silver chloride-containing grains whose exterior crystal faces lie in {111} crystallographic planes and are normal to axes of trigonal symmetry.
The term xe2x80x9cpBrxe2x80x9d=xe2x88x92log[Brxe2x88x92]
Cubo-octahedral grains with respect to high silver chloride-containing grains means fourteen-sided silver chloride-containing grains of which eight of the exterior crystal faces lie in {111} crystallographic planes and six of the exterior crystal faces lie in {100} crystallographic planes.
The grain making process is: the process of making grains that contains at least the nucleation phase (reacting a water-soluble silver salt and at least one water-soluble halide salt) and optional ripening and/or growth phases (addition of reagents).
Water Solubility: values are given at 25 degrees C. or at the nearest temperature to this where data are available. The solubility of solids is defined as the concentration of the compound in a solution that is in equilibrium with the solid phase at the specified temperature and one atmosphere pressure. For liquids whose water mixtures separate into two phases, the solubility given here is the concentration of the compound in the water-riche phase at equilibrium.
High chloride {111} crystal surfaces ({111} tabular and octahedral grains) can only be produced in the presence of a GGM. The reason for this is that high silver chloride {111} crystal surfaces, unlike high bromide {111} crystal surfaces, cannot be formed or maintained in the absence of a GGM, but rather take cubic forms, since {100} crystal faces are more stable in high silver chloride grains
High chloride grains with {111} crystal surfaces are of practical importance because they present a unique surface arrangement of silver and halide ions, which in turn influence the grain surface reaction and adsorption typically encountered in photographic applications. For high chloride {111} tabular grains a shortening of processing time is greatly desired and there is an urgent need for the development of silver halide.
GGM can be used to increase the aspect ratio for high bromide silver halide grain emulsions and to form tabular- and octahedral grains for high chloride silver halide grain emulsions.
The technology used presently in the prior art methods can be divided in three main groups:
According to the first method, high bromide {111} tabular grain emulsions are used.
The preparation of high bromide {111} tabular grain emulsions with the aid of GGM is mainly described in the patents: U.S. Pat. No. 5,411,851 (and EP 0,701,166); U.S. Pat. Nos. 5,411,853 and 6,418,125
In all these patents the composition of the {111} tabular grains depends on the composition of the grains from the initial crystallisation process, which is the nucleation phase. The patent (U.S. Pat. No. 5,411,851) disclose a method in which the ripened grains will be tabular, independent of the initial shape of the grains, when the initial thickness of the tabular grains after the nucleation phase is 0.06 xcexcm or less. During the nucleation phase the pBr is about 3.8. No additions of chemical reagents (silver nitrate nor potassium bromide) are performed to the reaction chamber after the nucleation phase, except for pH- and pBr-correction (e.g. pH=5.0 and pBr≈3.1). This means that the composition of the grain is determined by the reagents additions during the nucleation phase and can not be steered in one of the ripening phases (=physical- and/or Ostwald-ripening phases).
The main aspects of these known processes are:
U.S. Pat. No. 5,411,851: The GGM used in this patent are: tri-amino pyrimidine derivatives. The temperature during the nucleation phase is: =15xc2x0 C., and the pH range is: 4.6 less than pH less than 9.0.
U.S. Pat. No. 5,411,853 and EP 0,701,166: The GGM used in these patents are poly iodo phenol derivatives. The temperature during the nucleation phase is: 40xc2x0 C., and the pH range is: 1.5 less than pH less than 8.
U.S. Pat. No. 5,418,125: The GGM used in this patent are: hydroxy quinoline derivatives. The temperature during the nucleation phase is: =40xc2x0 C., and the pH range is: 2 less than pH less than 8.
According to Maskasky (U.S. Pat. Nos. 5,418,125; 5,411,851; 5,411,853 and EP 0 701 166 A1) it not understand why the grain growth process with double-jet precipitation of chemical reagents employing this grain growth modifiers are less effective than the grain growth process of his invention.
The process as described in prior art patents from Maeskssy is schematically described in FIG. 1.
The main disadvantages, for Maskasky""s system, as compared to the commonly used double-jet precipitation method, are:
1. The process described by Maskasky has only a nucleation stage in which silver and halide reagents are added. This implies that no grains with a shell layer having different halide compositions can be formed. Those core/shell grains are commonly employed in all photographic products because each layer can add to the unique photographic properties of the product. Therefore the double-jet method gives a better control over the crystal growth making process in which the photographic properties can be maximally utilised.
2. The used GGM are in general not very well soluble in water and can only be removed from the grains with special solvents and/or reduction of the pH (protonation), U.S. Pat. No. 5,418,125. The incomplete removal of the GGM from the grain surface will negatively influence the photographic properties. This will give an emulsion with higher fog or lower sensitivity. This is because spectral sensitizers can not effectively form aggregates onto the grain surface.
3. The manufacturing time to produce {111} tabular grains is increased from 1xc2xd-2 hour (for the double-jet precipitation method) to 2-17 hours.
The second method concerns the use of high chloride tabular grain emulsions
Without addition of GGM, silver chloride grains have {100} major faces, which lead to the formation of mainly cubic grains. With the addition of GGM, tabular silver chloride grains having {111} major faces are formed and the aspect ratio or, other grain properties of {111} tabular grains will depend on the GGM used. This is described in the following patents:
EPO 0 694 809 A1: The GGM used are phenol derivatives Because the water solubility of the phenol derivates is too low, a co-solvent has to be used for the addition of the GGM.
U.S. Pat. No. 4,804,621: The GGM used are amino pyrimidine derivatives. {111} tabular grains are formed with aspect ratios ranging from 5 till 9.
As the properties required for the crystal habit controlling agents, it is particularly important that the crystal habit controlling agent does not reduce the photographic sensitivity and does not hinder the adsorption of dyes for spectral sensitisation In this point, the use of the pyrimidines is undesirable The additionally used ammonia is increasing the solubility of the silver halide grains and makes it difficult to produce the practically useful small-sized tabular grains.
U.S. Pat. No. 4,983,508: The GGM used pyridine derivatives. Only 30% of the grains formed are tabular. The grains are suitable for rapid development processing with reduced fog.
U.S. Pat. No. 5,061,617: {111} tabular grains are formed with aspect ratios varying from 9 till 16, while the percentage of tabular grains vary from 30 till 70% with thiocyanate as GGM. However, a thiocyanate increases the solubility of silver chloride grains as the case of using ammonia.
U.S. Pat. No. 5,221,602: The GGM used are hydroaminoazines. Because the water solubility of the GGM is so low a co-solvent has be used for the addition of the GGM. The GGM can only be removed from the grains surface by an extra protonation step.
U.S. Pat. No. 5,286,621: The GGM are adenine derivatives of which adenine (C5H5N5) is the most effective. The GGM enhance the formation of {111} tabular silver chloride grains with aspect ratios ranging from 5 till 9. The GGM used are almost insoluble in water and can not be completely removed from the grain surface. In the most ideal case 10% of the adenine is still present on the grain surface after washing the emulsion. This causes a negative influence to the absorption of any spectral sensitisers at the grain surface.
U.S. Pat. No. 5,998,124: The GGM used are slightly water-soluble pyridine derivatives. At least 30% of the total grain projected area are accounted for by grains with {111} major faces.
According to the third method, high chloride octahedral grain emulsions are used.
The use of GGM may lead under specific conditions, like high GGM concentration and low addition rate of the reagents, to the formation of silver chloride grains with mainly octahedral shape. Those grains are bounded by {111} faces. This is described in patent U.S. Pat. No. 4,801,523, for an amino azapyridine as GGM. This GGM is poorly water dissolvable and a co-solvent should be used for the addition. However the low solubility will hinder the removal from the grain surfaces. This type of grains is of special interest for producing mono-disperse grain emulsions. As the properties required for the crystal habit controlling agents, it is particularly important that the crystal habit controlling agent does not reduce the photographic sensitivity and does not hinder the adsorption of dyes for spectral sensitisation. In this point, the use of the pyrimidines is undesirable.
For U.S. Pat. No. 5,221,602; EPO 0 694 809 A1; U.S. Pat. Nos. 4,983,508 and 5,286,621 the GGM are almost insoluble in water. Therefore, the interaction with the grain surface will be high and removal from the surface will be a problem which is illustrated by the incomplete removal of the GGM from the surface (U.S. Pat. No. 5,286,621) or the requirement of an additional step to remove the GGM from the surface (U.S. Pat. No. 5,221,602)
The patents: EP 0 651 284 A1; EP 0 561 415 A1, U.S. Pat. Nos. 5,879,874; 5,498,516; 5,482,826 and 5,418,124 disclose organic iodide compounds, that release very easily the iodide ion(s) at a certain pH, in reaction with a nucleophilic molecule, such that the iodide ion form together with silver a silver iodide layer onto the grains. In these iodide releasing stages no increase of the aspect ratio occur.
The present invention is primarily based on the usage of a grain growth modifier compound with a hydrocarbon backbone to which are attached one or more halide groups and at least one polar group (to increase the solubility). The other atoms/groups to the back bone can be freely chosen as far as they do not decrease the solubility too much This compound will be used as GGM for the preparation of silver halide {111} tabular and/or octahedral grain emulsions.
Another aspect of the invention is the formation of {111} tabular grains for high bromide emulsions with an increased aspect ratio of more than 4 and a more narrow grain size distribution wherein at least 50% of the total grain population are high bromide {111} tabular grains.
Still another aspect of the invention is the formation of high chloride {111} tabular grain emulsions with an aspect ratio of more than 3, using these good water-soluble GGM wherein at least 50% of the total grain population are silver chloride {111} tabular grains.
A further aspect of the invention is the preparation of high chloride silver halide emulsions {111} with octahedral grains wherein at least 50% of the total grain population are octahedral silver halide grains.
The present invention is accordingly directed to a method for producing a silver halide photographic emulsion comprising the step of reacting a water-soluble silver salt and at least one water-soluble halide salt containing chloride or bromide in aqueous solution in the presence of an organic Grain Growth Modifier (GGM) compound, containing a halide X, which halide is not released in the form of an ion, to form light-sensitive silver halide grains having a silver halide content of a least 50 mole %, said grain growth modifier compound being water-soluble with a solubility greater than 4 mmole per liter, and being selected from the group of compounds with a hydrocarbon backbone R to which is attached one or more halide groups and at least one polar group.
Other aspects and advantages of the present invention will become apparent from the following descriptions, taken into connection with the accompanying drawings, wherein, by way of illustration and example, an embodiment of the present invention is disclosed.